Describe Nervous mechanism of regulation of respiration & significance of dual control. Describe the different respiratory centres in brain stem with their interconnections & functions. Describe the genesis of basic rhythm of respiration Describe the clinical relevance of the nervous control of respiration

1. Regulation of Respiration

2. Objectives
• Describe Nervous mechanism of regulation of
respiration & significance of dual control.
• Describe the different respiratory centres in
brain stem with their interconnections &
functions.
• Describe the genesis of basic rhythm of
respiration
• Describe the clinical relevance of the nervous
control of respiration

3. Regulation of respiration achieved by two ways or
two mechanisms.
1)Nervous control mechanism,
2)Chemical control mechanism.

4. Neural regulation of respiration occurs by two
systems:-
a)System responsible for automatic control or
metabolic control of respiration:-
Situated in brainstem & concerned with O2 delivery
& acid base balance.
b)System responsible for Voluntary control or
behavioural control of respiration:-
Located in cerebral cortex.

5. Goal of Respiration
• To maintain normal arterial tensions of O2 &
CO2.
• Achieved by maintaining PO2 & PCO2 in alveoli
constant.
• Alveolar ventilation is maintained constant by
adjusting Pulmonary ventilation according to the
need of the body.

6. Pulmonary ventilation =Rate of resp x Depth of resp.
Normally 14-16/min 500ml
(Tidal volume).
So rate & depth of respiration is adjusted to
maintain normal arterial tensions of O2 & CO2.
Regulatory mechanisms adjust the Pulmonary
ventilation by controlling the movements of chest.

7. •Dual control has great functional significance.
•Involuntary or Automatic control of respiration
allows human to breathe without conscious effort
under all circumstances including sleeping & is
essential to life.
•Voluntary control of respiration facilitates acts
like talking, singing, swimming, breath holding &
voluntary hyperventilation.

8. Automatic control of respiration :-It regulates
respiration by several groups of neurons called as
Respiratory centres.
It includes :-1)Medullary respiratory centres,
2)Pontine respiratory centres &
3)Reticular activating system(RAS).

9. Medullary respiratory centres :- It includes
a)Pre Botzinger Complex(Pace maker cells),
b)Dorsal groups of neurons(DRG) &
c)Ventral groups of neurons(VRG)
Pontine respiratory centres :- It includes
a) Apneustic centre in lower pons &
b) Pneumotaxic centre in upper pons.

11. Pre-BOTC-Pacemaker cells in Pre Bot zinger
complex,IO-Inferior olive, NA-Nucleus Ambiguus
& LRN-Lateral reticular nucleus

12. NPBL-Nucleus parabrachialis(Pneumotaxic centre),
CP-cerebellar peduncle.

13. Medullary respiratory centres :-
1)Pre Bot zinger complex :- Situated between
nucleus ambiguus & lateral reticular nucleus.
Neurons(Pacemaker cells) are present in it.
They discharge spontaneously & rhythmically to
phrenic motor neurons of spinal cord.

14. Responsible for genesis of respiration.
Section or lesion between Pre Bot zinger
complex & phrenic motor neurons i.e between
medulla & spinal cord ceases respiration.

15. 2)Dorsal respiratory group of neurons(DRG):-
It is situated near & in the nucleus of Tractus
Solitarius.
It has primarily inspiratory neurons → impulses to
phrenic motors neurons →Inspiration during quiet
breathing.

16. Afferents to DRG:-
1)Peripheral chemoreceptors,
2)Baroreceptors &
3)Several types of receptors in
the lungs.
DRG neurons project to Pre Botzinger pacemaker
cells.
Section or lesion in DRG do not abolish
respiratory activity.

17. Functions of DRG :-
1)Spontaneous basic rhythm is generated here.
2)It mainly contains Inspiratory neurons which
emits rhythmical inspiratory discharge.
3)These discharges are called Inspiratory ramp
signal which are transmitted to primary
inspiratory muscle i.e diaphragm.

18. Ramp signal :-It is weak in the beginning , ↑
steadily in ramp manner for 2 sec called as
inspiratory ramp.
Ramp signal abruptly ceases for next 3 sec →
turns off the exitation of diaphragm & allows
elastic recoil of the lungs & chestwall to cause
expiration.

19. Muscles of expiration need not act, cessation of
activity of inspiratory muscles is enough.
Thus expiration is a passive process during quiet
breathing.
Advantage of ramp signal :- Results in steady ↑
in lung volume during respiration rather than
inspiratory gasp (abrupt distenion).

20. Inspiratory neurons of DRG are of 3 types:-
1)Central inspiratory activity (CIA) neurons.
Function:-Generate basic respiratory rhythm.
2)Inspiratory Off Switch(IOS) neurons :-
Responsible for terminating the respiratory ramp
so terminates the excitation of muscles of
inspiration.

21. 3)Integrator neurons:-They activate the inspiratory
off switch neurons.That means CIA neurons trigger
the IOS neurons through Integrator neurons & thus
terminate their own discharge.
This forms basic circuit of generation of resp
rhythm. CIA + Integrator neurons
_
IOS +

22. Ventral respiratory group of neurons (VRG):-
In medulla VRG lies 5mm ant & lat to the DRG.
VRG has both types of neurons Inspiratory &
Expiratory & have inhibitory connections to each
other.
These neurons are totally inactive during quiet
respiration.

23. When the respiratory drive for ↑ pulmonary
ventilation (forceful respiration) is required,
respiratory signals spill from DRG to VRG.
Stimulation of I-neurons →Inspiration.
Stimulation of E-neurons → expiration.
These neurons send signals to accessory muscles
of respiration especially during exercise.
VRG neurons project to Pre Botzinger Complex.
Section or lesion in VRG do not abolish respiratory
activity.

24. Pontine Respiratory Centres :-They modulate
or modify activity of medullary centres.
1)Apneustic centre: - Situated in lower part of
the pons.
Intrinsically active i.e it sends continous
impulses to inspiratory neurons of DRG.

25. It prevents switch off of the inspiratory ramp .
So there is Apneusis (deep & prolonged
inspiration).
This ↑ tidal volume & ↑ duration of inspiration.
It also sends impulses to Pneumotaxic centre.
Apneustic centre inhibited by the vagus &
Pneumotaxic centre.

26. 2)Pneumotaxic centre :-Situated in upper part of
Pons in the nucleus parabrachialis.
It sends inhibitory impulses back to Apneustic
centre,so Apneustic centre is inhibited & ceases to
send impulses to inspiratory neurons in DRG.
Pneumotaxic centre keeps the Apneustic centre in
check & thus shortens inspiration leading to
shallow & more rapid respiratory pattern.

27. By inhibiting Apneustic centre it indirectly controls
the switch off point of inspiratory ramp,thus
controls duration of respiration.
Strong signals from Pneumotaxic centre ↑ rate of
respiration to 30-40/min.

28. Thus Apneustic centre & Pneumotaxic centre
regulate the depth & rate of respiration respectively.
Reticular activiting system :-Stimulates the
respiratory centres to ↑ respiratory drive by affecting
state of alertness or wakefulness of brain.
During sleep RAS activity ↓,this ↓ respiratory drive,
↓ Alveolar ventilation so slight ↑ in arterial CO2
tension.

29. Genesis of basic rhythm of respiration :-
Pre Bot Zinger complex or according to some
authors Inspiratory neurons of DRG sends
spontaneous rhythmic discharge of impulses via
white matter of spinal cord (between lateral &
ventral corticospinal tracts) reach the motor
neurons of spinal cord.

30. These motor neurons via efferent nerves supply
the muscles of respiration.
Respiratory muscles control movements of chest
& adjust the ventilation according to the
requirements of the body.

31. Motor neurons of spinal cord show reciprocal
innervation.
That means when motor neurons to
inspiratory muscles are active, those for the
expiratory muscles are inhibited.

32. Thus agonist are excited & antagonist are
inhibited.Then vice versa i.e antagonists
activated & agonist inhibited.
All the respiratory centres are bilaterally
represented in the brain stem with same sided
control & freely communicate with each other.

33. Integrator neurons
Central Inspiratory
Activity (CIA)Inspiratory Off
Switch Neurons
Respiratory
muscles
Cerebral
Cortex
Apneustic
Centre
Vagal
afferentsPneumotaxic
Centre
+
+
++
+
_
_+
+__
Genesis of Respiration

34. DRG
Respiratory
muscles
Cerebral
Cortex
Apneustic
Centre
Vagal
afferentsPneumotaxic
Centre
+
-+
+
+
+__
Genesis of Respiration

35. Afferent Impulses To Respiratory centres
Respiratory centres
Higher control
Cerebral
cortex
Hypothalamus &
Limbic system
Chemical control Non Chemical
control
Afferent impulses guide the respiratory centres to
regulate the respiration.

36. Higher Control(Cerebral cortex)
Voluntary control system.
Pathway:-
Neocortex bypasses medulla
↓
Project directly on spinal respiratory neurons
↓
Control respiratory muscles voluntarily
↓
By facilitating acts like talking,singing, swimming,
breathholding & Voluntary hyperventilation.

37. Voluntary control is temporary as chemical
drive overrides the voluntary control system &
respiration is resumed involuntarily.
Hypothalamus & Limbic control system :- Pain
& emotional stimuli influence rate & depth of
respiration via Hypothalamus & Limbic system.
Chemical control system :- Central & Peripheral
chemoreceptors influence medullary & pontine
respiratory centres.

38. Non Chemical Control :-
1)Afferent impulses from Pulmonary stretch
receptors (Hering Breuer inflation inhibiting
reflex) :-
Inflation of lungs→stimulates stretch receptors in
the smooth muscles of the bronchial tree
→through vagus impulses →respiratory centres
→inhibition of respiration.
This reflex is present in lower animals,when tidal
volume exceeds more than 1-1.5 lit. Thus it
limits tidal volume.
It is protective reflex.

39. 2)Afferent impulses from J-Receptors :
J receptors discovered by an Indian Physiologist
A S Paintal in 1954.
J-receptors(Juxtapulmonary capillary receptors)
very close to capillaries. They are unmyelinated
vagal nerve endings stimulated by ↑ interstitial
fluid in conditions like Pulmonary congestion ,
odema, hyperinflation of lungs & chemical
irritants.

40. J response is seen as apnoea followed by
hyperventilation, bradycardia, hypotension &
weakness of skeletal muscles.
Physiological role of J-receptors :-After
exercise some fluid is entrapped in the alveolar
interstitial space → J receptors stimulated →
dyspnoea & ↓ skeletal muscles tone →
discourages exercise.

41. 3) Afferent impulses from Irritant receptors
in the mucosa of the respiratory tract :-
They are stimulated by smoke, noxious
gases & particulate matter in the inspired air.
They initiate:
a)Cough reflex
b)Sneezing reflex

42. c) Hering Breuer deflation reflex : Deflation of
lungs (Collapse of alveoli) → irritant receptors in
bronchial epithelium stimulated → yawning,
sighing → opening of collapsed alveoli again.
d)Deglutation reflex(Protective reflex):Pharyngeal
phase of swallowing →receptors send impulses
through Glossopharyngeal nerve →resp centres
inhibited which prevents entry of food in
respiratory tract.

43. Afferent impulses from Proprioceptors (muscles,
joints & tendons) :-During exercise ,change in the
position of different parts of the body stimulates
proprioceptors→inspiratory neurons stimulated →
↑ rate & depth of respiration.
After the delivery of newborn, if the baby doesn’t cry
immediately, the paediatrician patt or slap on the
back or legs of the baby to initiate its first breath by
stimulating resp centres via this reflex.

44. Afferent impulses from Baroreceptors :-
Rise in blood pressure
↓
stimulates baroreceptors
↓
via vagus & glossopharyngeal
nerves
↓ inhibites not only
vasomotor centre but also
respiratory centres
↓
apnoea e.g
high doses of adrenaline →adrenaline apnoea.

45. Afferent impulses from Thermoreceptors :-
Increase in body temperature
↓
stimulates warm receptors
↓ via
somatic afferent nerves impulses reaches
cerebral cortex
↓ stimulates
respiratory centres
↓
hyperventilation.

47. Section D:
Complete transection of the brain stem.
Stops all respiration (Apnoea).No change if vagi
are intact or cut.
Section A:
Transection above pons (Between pons &
midbrain).(Decerebration).
Regular breathing continues(Eupnoea).
No change if vagi are intact or cut.
Inference: Respiratory centres are situated in
the medulla & pons.

48. Section B:
Transection in the midpons :
Pneumotaxic centre cut off from Apneustic
centre. No check over Apneustic centre, so
overactive.
If vagi are intact they inhibit apneustic centre &
resp is regular & rhythmic but slower & deeper.
If Vagi are cut –Arrest of resp in inspiration i.e
prolonged & sustained inspiration ( Apneusis).

49. Section C :
Transection at Junction of pons & medulla.
Resp continues it is rhythmic (inspiration
followed by expiration) but irregular.
No change if the vagi are intact or cut.

50. References :
- Understanding Medical Physiology
-By RL Bijlani
-Text book of Medical Physiology
-By Indu Khurana
-Text book of Medical Physiology
-By Guyton & Hall
-Text book of Medical Physiology
-By A.K.Jain
-Review of Medical Physiology
-By Ganong
-Net Source (Pic & etc.)